The best idea would be to make up a wooden backing to hang on the wall with hooks or nails positioned so the sword will sit in the backing. This way you will avoid damaging the sword and you can take it down at any time you like

If you ever plan on swinging it around ot cutting anything with it, just be sure to check if it's stainless steel or spring steel. Stainless steel is very brittle in longer lengths and can snap like a twig. It's fine for shorter knives, and perfect for display items because it's much more resistant to rust.

It might hvae a sticker or something on it somewhere or your sister might know. Display swords and usable swords are very different beasts.

I have an english Bastard sword (functional), a typical katan/wakizashi combo (display, broke one once and found this out the hard way ) and other various weapons. To get my sword on the wall I drilled two nails in (long ones), and mounted the crosspiece on them. I used a clamp and hammer to bend the nails upwards before putting them in, so the sword wouldn't fall on my in my sleep (its at the foot of my bed ). As to the katana/wakizashi it came with a stand to mount them on.